This program project renewal application continues our multidisciplinary approaches to studying drugs of abuse. Dr. Law will determine the gene structure of the delta opioid receptor (DOR), including positions and sizes of introns and the nature of regulator elements. In the hope of understanding the molecular mechanism of opioid tolerance, Drs. Loh and Law will engineer deletions/substitutions in critical regions of DOR, including the C- terminus and third cytoplasmic loop, to determine the role of specific residues in this region and their phosphorylation state on regulation of the receptor activities and receptor level in response to chronic opioid agonist treatment. Reagents such as receptor antibodies and epitope tagged receptor will be developed for these studies. In the final renewal proposal, Dr. Conti-Tronconi will quantitate acetylcholine receptor in several non-neuronal tissues known to be affected by nicotine abuse, including upper respiratory tract, smooth muscle cells and endothelium of blood vessels. She will characterize these AChRs with respect to subunit composition, demonstrate the presence of ACh metabolizing enzymes, determine whether they mediate such functions as cell adhesion, motility and differentiation, and investigate the effects of nicotine abuse on these molecules.